Ch. 12.4 Mutations
Section Objectives:
• Categorize the different kinds of
mutations that can occur in DNA.
• Compare the effects of different
kinds of mutations on cells and
organisms.
Mutations

Any change in DNA sequence is called a mutation.

can be caused by errors in replication, transcription, cell
division, or by external agents.

If mutation occurs in gametes (sex cells) it will
be passed on to offspring

may produce a new trait or it may result in a protein that
does not work correctly.
the mutation results in a protein that is nonfunctional,
and the embryo may not survive
In some rare cases a gene mutation may have positive
effects.
Mutations

If mutation takes place in a body cell, it is
not passed on to organism’s offspring




Damage to a gene may impair the function of the cell
When that cell divides, the new cells also will have
the same mutation
Some mutations of DNA in body cells affect genes
that control cell division.
This can result in the cells growing and dividing
rapidly, producing cancer.
Mutations

Changes to DNA are called mutations
change the DNA
 changes the mRNA
 may change protein
 may change trait

DNA
TACGCACATTTACGTACG
mRNA
AUGCGUGUAAAUGCAUGC
protein
aa aa aa aa aa aa aa
trait
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Types of mutations

Changes to the letters (A,C,T,G bases) in
the DNA

point mutation



change to ONE letter (base) in the DNA
may cause change to protein, may not
frameshift mutation



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addition of a new letter (base) in the DNA
sequence
deletion of a letter (base) in the DNA
both of these shift the DNA so it changes how
the codons are read
big changes to protein!
Point Mutations

One base change

can change the meaning of the whole protein
THEFATCATANDTHEREDRATRAN
THEFATCARANDTHEREDRATRAN
OR
THEFATCATENDTHEREDRATRAN
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Does this change
the sentence?
A LITTLE!
Point Mutations

Missense mutation = changes amino acid
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGUAUGCGAGUGA
MetArgValTyrValCysGluStop
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Does
this change
the protein?
DEPENDS…
Sickle cell anemia

Hemoglobin protein in red blood cells
strikes 1 out of 400 African Americans
 limits activity, painful & may die young

Normal
round cells
Misshapen
sickle cells
Only 1 out of
146 amino acids
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Point Mutations

Silent mutation = no change to protein
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGCUUGCGAGUGA
MetArgValTyrAlaCysGluStop
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Does
The this
codechange
has
repeats
the protein?
in it!
Why not?
Point Mutations

Nonsense mutation = change to STOP
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Really destroyed
that protein!
AUGCGUGUAUAAGCAUGCGAGUGA
MetArgValStop
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Frameshift Mutations

Add or delete one or more bases

changes the meaning of the whole protein
THEFATCATANDTHEREDRATRAN
Does this change
the sentence?
A LOT!
Delete
Add one!
one!
THEFATCANTANDTHEREDRATRAN
OR
THEFATCAANDTHEREDRATRAN
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Frameshift Mutations

Addition = add one or more bases
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGUCAUGCGAGUGA
MetArgValTyrValMetArgValA
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Does this change
the protein?
A LOT!
Frameshift Mutations

Deletion = lose one or more bases
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGAUGCGAGUGA
MetArgValTyrAspAlaSerGA
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Does this change
the protein?
A LOT!
Causes of Mutations

sometimes a mistake in base pairing
during DNA replication.

many mutations are caused by factors in
the environment

Any agent that can cause a change in DNA
is called a mutagen.

Mutagens include radiation, chemicals, and
even high temperatures
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